The invention pertains to a solid bowl centrifuge for separation of solid-liquid mixtures, with a liquid runoff located on one end region of the rotary-seated basket shell and with thick matter outlet openings located at the other end region of the basket shell, and with a centrifuge housing holding the spun off thick matter and having a flowing drying gas, whereby within the centrifuge housing in the flight path of the spun off thick matter, there is a baffle cone surrounding the thick matter output openings at a distance and diverting the thick matter.
The combined centrifugal drainage and thermal drying of clarified sludge in one compact structural unit having the configuration of a solid bowl worm-gear centrifuge is known, e.g., from WO-A-93/00562 and also from EP-A-0 979 984. The worm gear centrifuge is used as a dispersing unit for a directly outlet-connected convection dryer operated with hot gas or drying gas, in such a manner that the solids outlet housing and also the entire, standard housing of the centrifuge is exposed to the flowing, drying gas and is used as a flow dryer. Thus the drained thick matter spun off centrifugally from the thick matter outlet openings of the centrifugal basket is swirled up in dispersed form by the drying gas into spiral paths and is separated from the drying gas outside the centrifuge in a cyclone.
In the known centrifuges of the kind described above, within the centrifuge housing in the flight path of the spun off thick matter, there is a fixed baffle cone surrounding the thick matter outlet openings of the basket shell at a distance. This baffle cone is designed as a conical ring whose slant inclined, Inner conical surface is Intended to divert the impacting thick matter roughly into an axial direction, so that the spun off thick matter will not impact directly against the inner wall of the centrifuge housing. But it turns out that especially in the case of sludges tending to stick, the tiny thick matter particles spun off radially at high velocity, remain stuck to the conical surface of the fixed-site baffle cone and can form agglomerates, so that the drying process and the centrifuge operation is adversely affected, so it has previously been proposed to provide co-rotating cleaning blades or scratch plates outside at the basket shell of the centrifuge in the region of the thick matter outlet openings. Cleaning strips of these cleaning blades have a close proximity to the conical surface of the fixed-site baffle ring and are intended to scratch off the baked-on thick matter from the conical surface. Except for the fact that a design of this kind is structurally complicated and results in an additional energy requirement, the lumps of scratched off thick matter impede an efficient drying and they disrupt a dependable operation of the centrifuge.
The invention is based on the problem of creating a solid-bow centrifuge for mechanical draining and subsequent thermal drying of sludges, in which the possibility of lumping or bake-on of finely dispersed thick matter spun off from the thick matter outlet openings is minimized or eliminated.
This problem is solved in a solid-bow centrifuge with properties in accordance with the present invention.
In the invented centrifuge, the baffle cone located within the centrifuge housing in the flight path of the spun off, dispersed thick matter and surrounding the thick matter outlet openings of the basket shell at a distance, is not fixed stationarily in place, but rather it rotates during operation of the centrifuge. Thus, the baffle cone can be separately seated on a rotation bearing and can rotate at the same rotational velocity and with the same rotation direction as the basket shell, but also at a different rotational speed and even with an opposing rotational direction, where the rotational direction and the rotational velocity of the baffle cone are adapted to the existing requirements. For simplicity, the baffle cone is attached to the basket shell and it rotates with it at the same rotational speed. In contrast to the fixed baffle cone, the rotating baffle cone does not decelerate the thick matter spun off from the thick matter outlet openings of the basket shell upon impact on the conical surface, but rather the thick matter arrives upon a conical surface rotating with a correspondingly large circumferential velocity, where it is accelerated outward in a slanting direction or axially at a slant. Thus, the longitudinal velocity component of the thick matter which results from the breakdown of the radial velocity of the spun off thick matter into a normal component perpendicular to the conical surface of the baffle cone and into the conical longitudinal component, and which ultimately causes the fast migration of the thick matter in the direction of the large diameter of the rotating conical surface, is increased significantly, i.e., the rotating baffle cone, due to its self-cleaning effect, prevents thick matter bake-on and it distributes the spun off, diverted thick matter in disperse form uniformly into the drying space of the centrifuge with the flowing, drying gas.
According to an additional property of the invention, the conical surface of the co-rotating baffle cone has several profilings or vanes distributed about the perimeter, which run from the small conical diameter to the large conical diameter. These vanes guide the thick matter very quickly onto the conical surface of the baffle cone toward its large diameter or to the outer edge, so that the thick matter does not remain resting upon the conical surface. If the vanes are curved backward when viewed in the rotational direction of the baffle cone, then the possibility of eddy formation by the rotating vane and of additional energy loss will be minimized.